With development of electronic technology, multi-rail switching converter having a plurality of switching circuits to provide a plurality of output voltages is widely used as power supply for many electronic devices. Constant ON time (COT) control is employed to control switching converter for fast transient response, simple circuit structure, and smooth mode transition. However, it is not easy to achieve phase interleaving for COT controlled multi-rail switching converter, since each rail switching circuit has different output voltage, different ON-time period, and different switching frequency. Factors making non-average distribution of phase-shift among each rail switching circuit are, for example, different load condition and different parasitic parameters, and as a result, input ripple of multi-rail switching converter increases and (Electromagnetic Compatibility) EMC performance becomes worse.
Thereby, a multi-rail switching converter having average phase-shift among each rail switching circuit is needed, even when each rail switching circuit has different circuit parameters.